The present application is related generally to systems and methods for preventing collisions between vehicles on railway systems and, in particular, to systems and methods for determining accurate locations of railway vehicles and/or for providing proximity warnings or brake applications when a collision threat is detected.
A long standing problem in the railway industry has been the competing interests of maximizing throughput on the railway system while maintaining sufficient separation of the vehicles to prevent collisions. Significant time and resources have been expended towards developing proximity detecting systems which alert vehicle operators to potential collision threats. The typical proximity detection system includes the capability of the system to take automatic action to stop the vehicle should the operator not take the required action in response to a proximity warning.
Generally, in such prior art systems the location, speed, direction of travel and identification number of each vehicle is collected. This information may then be analyzed to determine which vehicles present a collision threat to one another. Once a vehicle is determined to be a collision threat, the proximity detecting systems will issue a proximity warning once the trains come within a predetermined threshold distance to each other. For example, if a train is travelling northbound on a track towards point A and a second train is travelling southbound on the same track to point A, a prior art proximity detecting system would issue a proximity warning to each train as the trains got within a certain distance of one another. Similarly, if two trains were travelling on the same track in the same direction and the trailing train was travelling at a faster speed than the lead train, a proximity warning would be issued when the distance between the two trains decreased to a certain predetermined threshold distance.
A common characteristic of the prior art proximity detection systems is the automatic enforcement braking if the proximity warning is not acknowledged by the operator. For example, many prior art collision avoidance systems require that the operator acknowledge the receipt of the proximity warning within a certain amount of time or the proximity detection system initiates enforcement braking to cause the train to come to a complete stop.
Some prior art proximity detection systems require more than mere acknowledgement of the proximity warning. For example, one such prior art system requires the operator of the train receiving the proximity warning to establish voice communications with the identified collision threat train in order to satisfy the warning acknowledgement and prevent automatic braking of the train. See, for example, the Hsu U.S. Pat. No. 5,574,469 issued Nov. 12, 1996.
Another general characteristic of many of the prior art proximity detection systems is that there may be more than one predetermined threshold distance. For example, when two vehicles are determined to be a collision threat and come within some predetermined threshold distance, a proximity warning is issued to each vehicle. If the distance between the trains should subsequently decrease to a second predetermined threshold distance, a second proximity warning may be given. This second proximity warning may have associated with it some additional required action of the operator. For example, an operator of a train may receive a proximity warning when it is determined that his train and another train pose a potential collision threat to each other and the distance between the two trains has decreased to eight miles. The operator may be required to acknowledge the alarm by depressing an acknowledgement button. If the acknowledgement button is not depressed within a set amount of time of receiving the alarm, the train may initiate proximity enforcement braking commands automatically. If the operator acknowledges the proximity alarm but the distance between the two trains decreases to five miles, a second proximity warning may be issued. This second warning may have associated with it, required action from the operator in addition to acknowledging the alarm, such as reducing the speed of the train. In a similar manner, there may be multiple predetermined threshold distances each with an associated required operator action in order to prevent the proximity detecting system from initiating enforcement braking commands to slow the train.
In order to prevent continuous unwanted alarms and enforcement actions in an area where trains are commonly within the proximity warning threshold (i.e., railyards) it is common for the prior art systems to offer a method of allowing the operator to manually disable the proximity detection system. However, the ability to disable the proximity detection system may lead to the inadvertent disablement of the system when the train leaves an area of congestion. Additionally, because of the severity of the resulting action if a proximity alarm is not acknowledged, there may also be situations when the vehicle operator would prefer to receive a proximity warning but would want to prevent an enforcement action.
A significant decrease in the net worth of a proximity detection system occurs if the system can not minimize false alarms. This is particularly true if the false alarm leads to an enforcement action which may have ramifications to the schedules of the entire railway system. For example, a vehicle that is following another vehicle at approximately the same speed and at a distance approximately equal to one of the predetermined threshold distances may cause a proximity alarm if the vehicle closes to less than the threshold distance. The alarm may clear if the trailing vehicle falls beyond the threshold distance. If the trailing vehicle subsequently closes within the threshold distance again a second proximity alarm would then be received. Without some method of screening out those situations where a continuous alarm may be expected, the operator may become desensitized to the importance of the proximity alarm. As a result, the operator may not acknowledge the "expected" alarm, inadvertently resulting in an enforcement action and unscheduled stopping of the vehicle.
Inherent in the operation of railed vehicles is conflict with not only other vehicles on the railway system but also non-railway system vehicles whose path may cross the path of a vehicle system on a railway (i.e., a railway crossing which allows automobiles to cross over the train tracks). Various systems have been developed which will warn the non-railway vehicle of the impending approach of the railway system vehicle.
Generally, in such prior art systems, a wayside centric approach is taken to warn vehicles of an approaching train. For example, a train may continuously transmit a signal at a predetermined signal strength along the direction of movement of the train. Wayside receivers located at the railway crossing will receive the signal as the train approaches the crossing. When the signal is received, the wayside unit may cause warning bells to ring, or warning lights to activate or crossing gates to close (or any combination of the three). Upon seeing and/or hearing the warning signals, an operator of a non-railway vehicle will know a train is approaching the crossing. While this warning system has proven effective at rail crossings, it is not an effective method of preventing collisions between vehicles where both vehicles are travelling on the same track. For instance, one characteristic of the prior art warning systems of this type, is that the actual location of the train is not determined nor utilized. Rather the relative location of the train with respect to the crossing is instrumental in activating the warning system. The warning signal transmitted by the train is usually a fixed signal of sufficient range to take into account expected propagation losses such that even in a worst case propagation loss environment, the warning signals will be activated in sufficient time to warn and/or prevent non-railway system vehicles from colliding with the train at the crossing.
Unlike the previously described proximity warning systems which are utilized to warn non-railway system vehicles of the approach of a railway vehicle, a proximity detection system that prevents collisions between railway system vehicles requires the accurate determination of location of each vehicle in the railway system. A system that can not accurately determine the location of the vehicles, will be forced to factor in a large margin error to ensure that collisions do not occur and as a result the vehicles will be spaced more than they need to be, thereby reducing throughput on the railway system.
It is known in prior art railway proximity warning systems for the system to display to the operator of the locomotive the location of the locomotive, and of other potentially conflicting locomotives. Generally, such locations are determined and displayed in geographic coordinates, such as latitude and longitude. In some situations, the system may also display the distance between the various locomotives, often calculating the distance based on the signal strength of the location signals received from other locomotives or from the geometric relationship between the geographic coordinates of the locomotives. Use of signal strength as the measure of distance between locomotives is often beset with varying signal transmission difficulties which may make more difficult an accurate determination of the actual distance between the locomotives. Moreover, in both signal strength and geometric calculations, the measure of the distance between the locomotives is usually a "line of sight" distance. Such a measure may be sufficient when the locomotives are on relatively straight sections of the same or parallel track; but, where the track has a considerable curvature, the distance along the track between two locomotives may be somewhat different from the line of sight distance. Because the criticality distance between locomotives is usually the distance "along the track", a system which uses merely signal strength or geometric calculations may signal an alert when none is necessary; i.e., while the locomotives are within the threshold distance of each other along the line of sight, they are further apart as measured along the track.
Prior art location determination systems (LDS) disclose various methods for determining the location of vehicles on a railway system. Wayside units and local detectors are well known systems in the prior art and provide an accurate location of railway vehicles, but the detection systems are expensive to acquire, install, and maintain, particularly in harsh environments.
LDS systems using satellite based systems are also well known. The Global Positioning System (GPS) and other satellite based location determining systems have been available and in use for a number of years (the term GPS is used hereafter to denote any positioning system which uses satellites and has capabilities similar to those of the GPS system.) Use of GPS systems with a wide variety of vehicles, including trains, is known to the field. Also known to the field are the inherent limitations of GPS use.
An accurate GPS location determination requires a GPS receiver to receive signals from four different GPS satellites. A train or any other vehicle can easily receive signals from the four required satellites if the vehicle is located in an open area, free of signal obstructions. For this reason, ships at sea and airplanes in flight are well positioned to make full use of GPS to accurately determine their location. A train located in an open area can similarly receive signals from the required four satellites. However, trains are not always so conveniently located.
The very nature of train travel is such that trains will be found in locations where they cannot easily receive from four satellites. Trains travel next to tall, signal obstructing structures, both natural and man-made. Trains travel through canyons and other areas which interfere with signal reception. As such, trains are often in the situation, unique from some other forms of mass and freight transit, in which they can receive signals from fewer than the required four satellites, and frequently can receive signals from only two satellites.
Obviously, there are other methods for determining the location of a vehicle. Particularly with respect to rail-based transportation, it is possible for a vehicle to have access to a database of information pertaining to rail routes whose locations are fixed and known. Such a database may be used to provide a way of converting elapsed distance from a known point along a known route into a location in two or three dimensional coordinates.
Such a system is well suited to rail vehicles by virtue of the fact that these vehicles cannot stray from their fixed and known tracks. The advantages of such a system are limited by its logistics, however. In order to know the distance traveled from a fixed point, an odometer type of measurement must be taken. Such a measurement is generally taken by counting wheel rotations, which is fraught with inaccuracies: wheels slip on rails, potentially both during acceleration and braking; wheel diameter changes over time as wheels wear down and develop flat spots; any wheel rotation measurement and calculation method is inherently at least partly mechanical, thus subject to mechanical problems; all such measurements are based on correctly resetting a counter at a designated zero point from which such measurements are taken, which might not be easily performed; and independent of the ability to measure distance travelled, the entire system is subject to the accuracy of the initial database upon which the final location determination is based.
It is desirable to combine the best features of satellite based and elapsed distance based location determination methods. Such a system could approximate a rail vehicle's location based on a track database to within some range of error. This estimate could be used as the basis for a satellite based measurement which takes into account not only the estimated location of the rail vehicle, but also the relative location of nearby geosynchronous satellites. Such a system need not have access to the full four satellites normally required.
While the typical prior art location determination systems require three or more satellites to achieve the accuracy required to efficiently plan train movement, recent developments in technology have allowed accurate location determination system with fewer than three satellites. A further explanation of how to determine location with as few as two satellites is disclosed in the Zahm et al. U.S. patent application Ser. No. 08/733,963, filed Oct. 23, 1996, entitled "Application Of GPS To A Railroad Navigation System Using Two Satellites And A Stored Database", to which this application is a continuation-in-part application.
Most prior art location determination systems are unable to distinguish between parallel tracks situated close together. For example, a train may be directed to a siding for a planned "meet and pass" with another train. Because the siding is parallel and located adjacent to the main track, the typical location determination system can not determine whether the train is on the main track or the siding. If this location position was then entered into a proximity warning system, the proximity system may indicate a collision situation between two trains, when in actuality the trains are correctly positioned for a meet and pass.
Because the typical proximity detection systems determine the location of each vehicle, it is possible to calculate the "line of sight" distance between the vehicles. This distance combined with the speed and direction of each vehicle enables the proximity detection systems to determine which vehicles pose a collision threat to each other. However, the collision threat determination of the typical prior art system may not always be accurate. For example, the determination of the actual location of two trains will permit the "line of sight" distance between the two trains to be determined. However, because the trains are constrained to operate on railway tracks, and the railway tracks may not run in a straight line between the two trains, the actual track distance between the two trains may differ significantly from the "line of sight" distance. Similarly, some prior art proximity detection systems do not take into account that the vehicles may be travelling on separate non intersecting tracks so that although the vehicles appear to be travelling towards each other, there is no opportunity for a collision because they are on separate tracks.
Regardless of the type of LDS system used, the location of the vehicles on the railway system is necessary component in the typical proximity detection system. The more accurate the location determination, the more closely that vehicles can be positioned together because the margin of error is reduced without having to account for the uncertainties of vehicle locations.
Accordingly, it is an object of the present invention to provide a novel of method and system for controlling railway vehicles which obviates these and other known difficulties in collision avoiding and location determining systems for railways.
It is a further object of the present invention to provide a novel of method and system for controlling railway vehicles which increases the throughput of vehicles on a railway system while minimizing collisions between the vehicles.
It is another object of the present invention to provide a novel method and system for controlling railway vehicles which determines the track distance between vehicles on a railway system.
It is yet another object of the present invention to provide a novel method and system for controlling railway vehicles by automatically disabling the alarming and the enforcement function of a proximity detection system based upon the location or the speed of the vehicle.
It is still another object of the present invention to provide a novel method and system for controlling railway vehicles by manually disabling the enforcement function of a proximity detection device without disarming the warning feature.
It is a further object of the present invention to provide a novel method and system for controlling railway vehicles by reducing the number of expected alarms received from the proximity detection system.
It is yet a further object of the present invention to provide a novel method and system for controlling railway vehicles by differentiating railway vehicle locations between closely positioned track paths.
It is still a further object of the present invention to provide a novel method and system for controlling railway vehicles by improving the accuracy of their location determination systems.
It is yet another object of the present invention to provide a novel method and system for determining and displaying railway vehicle information consistent with railway operating practices.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.